ON THE CONDUCTIVE POWEES OF VAEIOUS SUBSTANCES. 
819 
.Another block of harder sandstone than the preceding gave, when dry, 
when its weight was 
When moist, it gave 
its weight being then 
after the experiment. 
9221-5 grains. 
9434 grains 
And again, when saturated with moisture, it gave 
its weight being 
9547 grains 
after the experiment. The temperature of the lower surface of the block in each of 
these experiments was 211°-0. 
We have the same conclusion here as with the chalk — that an increase of conduc- 
tivity is produced by an increase of moisture, but that the conductivity ceases to increase 
considerably before we arrive at the state of saturation, when it would appear to be 
somewhat less than its maximum value. We have also the same conclusion from a 
similar experiment on a block of sandstone from the Millstone Grit, and made at like 
temperatures with the preceding one. It gave, when dry. 
and then weighed 
When moist, 
and it weighed 
When saturated, 
its weight being 
- = •55, 
/» " 
8999-5 grains. 
-=•65, 
c ’ 
9210 grains. 
-=•61, 
c ’ 
9291 grains. 
The quantity of water absorbed in both these last cases was much less than in the Chalk 
and New Red Sandstone, as well as the effect on the conductivity. 
(3) Argillaceous Mocks . — A block of very dry clay gave 
and a moist block gave 
